The history of life has been punctuated by brief episodes of mass extinction. The five major ones ended the Ordivician Devonian, Permian, Triassic, and Cretaceous eras (see fig ure below ). A general pattern was found when the extinctions were studied: 1. Extinction strikes in both the land and the sea. 2. On the land, while animals suffer repeatedly, plants tend to be highly resistant to mass extinctions. 3. Preferential disappearance of tropical forms of life during mass extinctions. 4. …showed first 75 words of 1735 total…

…showed last 75 words of 1735 total…and paleontological community that a giant impact did occur, there is still debate about its effect on the Earth's biota. This debate breaks down into two categories. 1. Is the pattern of extinctions actually compatible with an impact? 2. Were there other things going on that might have contributed to the extinctions, or even been more important? Scientists are closer than ever at solving these mysteries with the help of models that simulate the event. ------------------------------------------------------------------------ **Bibliography**